The organizations that remediate Superfund sites face the challenge of how to measure success; i.e., how to assess the changes in the bioavailability of contaminants.They need quantitative tools that can characterize contaminants and predict their risk to local organisms and humans. Non-chemical factors such as ultra-violet radiation can transform the parent compounds into unmonitored chemicals that can change the toxicity of waters and sediments. To address this issue, we have developed passive sampling devices (PSDs) that can sequester thousands of bioavailable chemicals. These devices can help regulatory agencies to evaluate new remediation technologies that may either produce or release previously unmonitored chemicals. Our PSDs are now sequestering chemicals at multiple Superfund sites, where they capture relevant organic compounds, including hydrophilic and semi-polar contaminants. We propose to test these hypotheses: PSDs sequester realistic and relevant mixtures from Superfund sites. PSDs can help researchers to characterize exposure accurately. PSDs can simplify toxicity assessments. PSDs can evaluate the effectiveness of remediation, considering not only the target contaminants but also any perturbations of the system that the remediation technologies may have induced. PSDs can serve as biological surrogates in public health assessments of Superfund sites. We propose to develop a set of widely applicable bio-analytical tools. We will integrate these tools with bioassays to characterize Superfund sediments. We assume that a small minority of the chemicals at Superfund sites are responsible for the majority of the toxicity. We will apply stressors to PSD extracts and characterize the chemical and biological effects. We will deliver methods and tools to assess the impact of non-chemical/chemical stressors that act on Superfund mixtures during natural transformation processes and remediation. We will develop PSD-bioaccumulation models that can predict chemical load in aquatic tissues with useful accuracy on the basis of measured PSD extracts. The ability to predict aquatic tissues from PSD extracts will enable Superfund managers and public health officials to collect data with better temporal and spatial resolution.